Microelectromechanical structures (MEMS) and other microengineered devices are presently being developed for a wide variety of applications in view of the size, cost and reliability advantages provided by these devices. Many different varieties of MEMS devices have been created, including microgears, micromotors, and other micromachined devices that are capable of motion or applying force. These MEMS devices can be employed in a variety of applications including hydraulic applications in which MEMS pumps or valves are utilized and optical applications which include MEMS light valves and shutters.
MEMS devices have relied upon various techniques to provide the force necessary to cause the desired motion within these microstructures. MEMS devices are driven by electromagnetic fields, while other micromachined structures are activated by piezoelectric or electrostatic forces. Recently, MEMS devices that are actuated by the controlled thermal expansion of an actuator or other MEMS component have been developed. For example, U.S. patent application Ser. Nos. 08/767,192; 08/936,598, and 08/965,277 which are assigned to the assignee of the present invention, describe various types of thermally actuated MEMS devices. The contents of each of these applications are hereby incorporated by reference herein. Thermal arched beam (TAB) actuators as described in these applications comprise arched beams formed from silicon or metallic materials that further arch or otherwise deflect when heated, thereby creating motive force. These applications also describe various types of direct and indirect heating mechanisms for heating the beams to cause further arching. The aforementioned thermal actuators are designed to move in one direction, i.e., in one dimension. Further, arrays of thermal actuators are typically used to increase the amount of actuation force provided. While these thermally actuated MEMS devices may be used in a variety of MEMS applications, such as MEMS relays, valves and the like, some applications for MEMS thermal actuators require other types of displacement, such as motion in two or three dimensions.
Thermally actuated MEMS devices capable of motion in two or three dimensions have been developed. For example, Lucas NovaSensor of Fremont, Calif. has developed a variety of thermally actuated MEMS devices capable of moving in either two or three dimensions. The devices capable of movement in two dimensions typically comprise one or more arched beams that deflect within a plane in response to thermal actuation. The devices capable of movement in three dimensions are disposed within a plane parallel to the substrate when not thermally actuated. Once thermally actuated, these devices are moved out of this plane, such as by rotating or lifting out of the plane. Another class of thermally actuated devices designed for out of plane movement are disposed out of plane when not thermally actuated. For example, these devices include the thermally actuated devices described by U.S. Pat. No. 5,796,152 to Carr et al., and U.S. Pat. No. 5,862,003 to Saif et al. These devices typically have one end affixed to the substrate and another end free to move in response thermal actuation. Because of this design, the relative amount of movement out of plane is limited. In addition, while all the aforementioned devices can be disposed in an array, the amount of movement produced by the array is not increased proportionately to the number of devices that have been combined into the array.
While thermally activated MEMS structures able to move in one, two, and three dimensions have been developed, it would still be advantageous to develop devices better optimized for increased amounts of movement in these directions. For example, it would be advantageous to provide thermally actuated MEMS devices that could be scalably arrayed so as to correspondingly combine the displacement of individual devices within the array, thereby providing much greater displacement than conventional MEMS devices. Further, it would be advantageous to provide improved thermally actuated MEMS devices that could move along more than one dimension in response to thermal actuation thereof. For example, improved thermally actuated MEMS devices capable of relatively large displacement both in plane and out of plane are needed both for new applications and to better serve existing applications.